Giardiasis in Bergen. Outbreak and clinical consequences.

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Background
Giardia lamblia is a common cause of waterborne disease. It is endemic in many
parts of the world, especially where sanitation is poor, but in Europe and North
America it is most often encountered in outbreaks following contamination of
drinking water. The first registered outbreak of giardiasis affecting a large community
in Norway happened in Bergen in the autumn of 2004. The reservoir “Svartediket”
was the source, and the water probably held Giardia cysts for several weeks.
Giardia can cause acute and chronic gastroenteritis. Several drugs constitute effective
treatment, and metronidazole is the main drug available in Norway. Prior to the
outbreak in Bergen there were no published studies on long term effects after
eradication of the parasite.
Aims
The aim of the studies in this thesis is to investigate the course of giardiasis and its
consequences following a large outbreak in an area where Giardia is not endemic.
Methods
In the first study, we concentrated on patients from general practice. Patients with
clinically defined giardiasis were identified through a search in the medical records at
two general practice clinics located in the area receiving water from the contaminated
reservoir. Of the 7,100 persons registered, 134 fulfilled the inclusion criteria and 119
consented to take part in the study. Data were retrospectively obtained from the
medical records. The patients were then requested to complete a mailed questionnaire
and submit stool samples six months after the outbreak. A second questionnaire was
sent out one year after the outbreak. The main outcome variable was abdominal
symptoms that were not present prior to the acute infection. In the second study, we investigated a historic cohort of 1252 patients with giardiasis
verified by detection of Giardia in stool samples submitted as part of regular clinical
investigations in Bergen during the outbreak. A 2:1 control group matched by age and
gender was recruited from the general population of Bergen. This group was later
expanded so that the whole control group consisted of 3594 individuals. All
participants received a questionnaire by mail three years after the outbreak. Main
outcome variables were irritable bowel syndrome (IBS) according to Rome III criteria
and “chronic fatigue” as defined by the Fatigue Questionnaire.
Results
In the group of patients from general practice the majority was between 20 and 39
years of age (51.4%), and there were more women (69.3%) than men. The diagnosis
was supported by a positive test for Giardia lamblia in 55% (66/119) of the patients.
Treatment with metronidazole was given to 89 (75%), and after initial treatment 36%
(32/89) returned to their doctor because symptoms recurred. A second prescription
was given to 28% (25/89), after which 16% (14/89) returned once more. 11% (10/89)
received a third treatment with metronidazole. Six months after the outbreak stool
samples were positive for Giardia in three of 82 patients. At this point 37% (44/118)
reported gastrointestinal symptoms related to their Giardia-infection, and after 12
months this proportion was 19% (19/99).
In the cohort of patients with laboratory verified giardiasis the prevalence of IBS
three years after the outbreak was 46% (355/770), compared to 14% in the control
group. The adjusted relative risk (RR) was 3.4 (95% confidence interval (CI) 2.9 to
3.8). The prevalence of chronic fatigue was 46% (366/794) among the Giardiapatients,
and 12% among the controls, giving an adjusted RR of 4.0 (95% CI 3.5 to
4.5). IBS and chronic fatigue were associated, but there was also an increased risk of
having IBS only (RR 1.8, 95% CI 1.4 to 2.3) or chronic fatigue only (RR 2.2, 95% CI
1.7 to 2.8). Discussion
In the study from general practice we identified patients that would have been missed
by a strict laboratory based inclusion criterion, either because stool samples were not
submitted or due do misclassification when samples were negative. Several patients
did not receive treatment and this could suggest that they did not have giardiasis, but
another reason could be that they called at the medical centre before the outbreak was
known and recovered spontaneously without treatment. After clearance of the
parasite a substantial proportion of the patients had persisting symptoms 6 and 12
months after the outbreak, which shows that potential negative health effects of
giardiasis was more extensive than first anticipated.
In the cohort of persons with verified giardiasis the infection was associated with a
high prevalence of IBS and chronic fatigue three years after the outbreak, and the risk
was significantly higher than in the control group. This supports the findings in the
group from general practice, and shows the consequences in a larger population and
over a longer period of time. The prevalence of IBS in this study and gastrointestinal
symptoms in the first one differs, but cannot be easily compared. The sample sizes
vary, the case definitions are different and the questionnaires used to define the
outcomes are not the same. Put together the two studies illustrate a wider range of the
clinical consequences after the outbreak.
Conclusions
These studies show that a considerable proportion of patients consistently had
persisting symptoms after giardiasis from the time of the acute infection and up to
three years after. The association between acute giardiasis and later gastrointestinal
symptoms and fatigue is strong. This calls for more research on the mechanisms for
both giardiasis and medically unexplained physical symptoms like IBS and chronic
fatigue.

Har del(er)

Paper I: Wensaas KA, Langeland N, Rortveit G. Prevalence of recurring symptoms after infection with Giardia lamblia in a non-endemic area. Scandinavian Journal of Primary Health Care 27: 12-17, 2009. Full text not available in BORA due to publisher restrictions. The article is available at: http://dx.doi.org/10.1080/02813430802602393

Paper II: Wensaas KA, Langeland N, Rortveit G. Post-infectious gastrointestinal symptoms after acute Giardiasis. A 1-year follow-up in general practice. Family Practice 27(3): 255-259, March 2010. Full text not available in BORA due to publisher restrictions. The article is available at: http://dx.doi.org/10.1093/fampra/cmq005